Enhanced node b and method for precoding with reduced quantization error

ABSTRACT

Embodiments of an enhanced Node B (eNB) and method for precoding with reduced quantization error are generally described herein. In some embodiments, first and second precoding-matrix indicator (PMI) reports may be received on an uplink channel and a single subband precoder matrix may be interpolated from precoding matrices indicated by both the PMI reports. Symbols for multiple-input multiple output (MIMO) beamforming may be precoded using the interpolated precoder matrix computed for single subband for a multiple user (MU)-MIMO downlink orthogonal frequency division multiple access (OFDMA) transmission. In some embodiments, each of the first and second PMI reports includes a PMI associated with a same subband that jointly describes a recommended precoder.

PRIORITY CLAIM

This application is a continuation of U.S. patent application Ser. No.14/887,499, filed on Oct. 20, 2015, which is a continuation of U.S.patent application Ser. No. 14/160,931, filed on Jan. 22, 2014, nowissued as U.S. Pat. No. 9,197,372, which is a continuation of U.S.patent application Ser. No. 13/075,320, filed on Mar. 30, 2011, nowissued as U.S. Pat. No. 8,644,289, which claims priority under 35 U.S.C.119(e) to U.S. Provisional Patent Application Ser. No. 61/410,740, filedNov. 5, 2010, all of which are incorporated herein by reference in theirentireties.

TECHNICAL FIELD

Embodiments pertain to wireless communications. Some embodiments relateto codebook interpolation to reduce quantization error for closed-loopmulti-user multiple-input multiple output (MU-MIMO). Some embodimentsrelate to codebook interpolation for the various reporting modes of thephysical uplink control channel (PUCCH) and the physical uplink sharedchannel (PUSCH) of the Evolved Universal Terrestrial Radio AccessNetwork (E-UTRAN), known as the Long Term Evolution and referred to asLTE.

Some embodiments relate to codebook interpolation for the LTE PUCCHconfigured for reporting mode 2-1 extension, and other embodimentsrelate to codebook interpolation for the PUSCH configured for reportingmodes 3-1 and 3-2 of LTE release 10 (known as LTE advanced).

BACKGROUND

Fourth-Generation (4G) communication systems, such as LTE networks, useclosed-loop beamforming techniques to improve throughput. In thesesystems, a receiver feeds back, among other things, precodinginformation, to a transmitter that recommends a precoder for use intransmitting beamformed signals back to the receiver. Since theselection of precoders is limited to particular codebooks, therecommended precoder may not be ideal based on the current channelconditions. MU-MIMO transmissions are particularly sensitive to thisquantization error for a given codebook. Although this quantizationerror may be reduced through the use of a larger codebook, recommendinga precoder associated with a larger codebook would require significantadditional feedback as well as defining a larger codebook.

Thus, what are needed are systems and methods for precoding that reducequantization error without the use of larger codebook. What are alsoneeded are systems and methods for precoding that reduce quantizationerror suitable for MU-MIMO in LTE networks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional diagram of enhanced node-B (eNB) in accordancewith some embodiments;

FIG. 2 is a functional block diagram of user equipment (UE) inaccordance with some embodiments;

FIG. 3 illustrates Discrete Fourier Transform (DFT) vectors associatedwith precoding matrices in accordance with some embodiments;

FIG. 4 is a flow chart of a procedure for generating and reporting firstand second precoding matrix indicators (PMIs) in accordance with someembodiments;

FIGS. 5A and 5B illustrate examples of transmissions on the PUCCHconfigured for reporting mode 2-1 extension in accordance with someembodiments;

FIGS. 6A through 6G illustrate examples of transmissions on the PUCCHconfigured for reporting mode 3-1 in accordance with some embodiments.

DETAILED DESCRIPTION

The following description and the drawings sufficiently illustratespecific embodiments to enable those skilled in the art to practicethem. Other embodiments may incorporate structural, logical, electrical,process, and other changes. Portions and features of some embodimentsmay be included in, or substituted for, those of other embodiments.Embodiments set forth in the claims encompass all available equivalentsof those claims.

FIG. 1 is a functional diagram of enhanced node-B (eNB) in accordancewith some embodiments. The eNB 102 may be configured to receive firstand second precoding-matrix indicator (PMI) reports 103 on an uplinkchannel from user equipment (UE), and compute a single subband precodermatrix (W₂) 105 from both the PMI reports 103. The eNB 102 may also beconfigured to precode symbols for MIMO beamforming using the computedsingle subband precoder matrix 105 for downlink transmission to the UEwithin a subband. Each of the first and second PMI reports 103 includesa PMI associated with a same subband (SB). The first PMI report mayinclude a first subband PMI and the second PMI report may include asecond subband PMI. In these embodiments, the use of two PMIs associatedwith the same subband may help reduce quantization error without havingto define a new codebook. These embodiments are described in more detailbelow.

As illustrated in FIG. 1, the eNB 102 may include, among other things, aprecoder matrix interpolator 104 to generate an interpolated precodingmatrix corresponding to the single subband precoder matrix 105 computedfrom the PMIs in both the PMI reports 103. The eNB 102 may also includephysical layer (PHY) circuitry 106 to precode symbols for beamformingfor the downlink transmission 107. The eNB 102 may also include two ormore antennas 101 for MIMO as well as MU-MIMO communications. In someembodiments, the MIMO transmission may be transmission on a physicaldownlink shared channel (PDSCH).

FIG. 2 is a functional block diagram of user equipment (UE) inaccordance with some embodiments. The UE 202 may include a PMI generator204 configured to select the first and second PMIs based on channelconditions within a particular subband, and physical-layer circuitry(PHY) 206 to transmit the PMI reports 103 (FIG. 1) to the eNB 102 (FIG.1). Each PMI in the PMI reports 103 may be associated with a precodermatrix. The UE 202 may also include two or more antennas 201 for MIMOcommunications as well as for the receipt of MU-MIMO communications.

In accordance with some embodiments, the second subband PMI is selectedby the UE 202 after selecting the first subband PMI by searchingcandidate precoder matrices that, when combined with a precoder matrixindicated by the first subband PMI, result in a more accurate precoderfor the subband. In other words, the use of the computed single subbandprecoder matrix 105 by the eNB 102 results in a more accurate precoderfor the subband than the precoder resulting from use of precoder matrixindicated by the first subband PMI by itself. In some embodiments, theUE may generate candidate single interpolated subband precoder matricesby combining the first precoder matrix with candidate second precodermatrixes to identify a selected second precoder matrix that whencombined with the first precoder matrix results in a single interpolatedsubband precoder matrix that provides a maximum reduction inquantization error when used by the eNB 102 for precoding transmissionsto the UE.

A subband may be one resource block (RB) that comprises a set ofsubcarriers (e.g., twelve subcarriers), although this is not arequirement. In some embodiments, the first subband PMI and the secondsubband PMI may both be selected by the UE 202 from a table depending onthe transmission rank.

In some embodiments, the UE 202 selects a first precoder matrix for thefirst subband PMI from a set of precoder matrices defined by a codebookto maximize throughput based on a channel transfer function associatedwith the subband. The UE 202 selects a second precoder matrix for thesecond subband PMI so that the interpolated precoder matrix computedfrom both the first subband PMI and the second subband PMI reducesquantization error that would result from use of the precoder matrixindicated by the first subband PMI alone.

In these embodiments, single subband precoder matrix that is computedfrom both the first subband PMI and the second subband PMI is arecommended precoding matrix (i.e., recommended by the UE 202 to the eNB102). Although the precoder matrix indicated by the first subband PMImay be selected to maximize throughput, the use of this precoder matrixmay result in a quantization error that may be large depending on thedifferences between an optimum precoder and the precoder associated withthe first subband PMI.

FIG. 3 illustrates Discrete Fourier Transform (DFT) vectors associatedwith precoding matrices in accordance with some embodiments. Asillustrated in FIG. 3, DFT vector 306 may be associated with an optimumprecoder for the subband and DFT vector 302 may be associated with theprecoder associated with the first subband PMI (W₂). The differencebetween DFT vectors 302 and 306 may correspond to the quantization errorthat would result without the use of the second subband PMI. DFT vector304 may be associated with the second subband PMI, and DFT vector 308may be associated with the interpolated single subband precoder matrixcomputed from both the first subband PMI and the second subband PMI. Asa result, the quantization error may be reduced to the differencebetween DFT vectors 306 and 308, resulting in reduced quantization error305.

In some embodiments, the first PMI report includes a subband PMI, andthe second PMI report includes a subband differential PMI. The subbandPMI may be an index corresponding to a recommended precoder based onchannel characteristics of the subband. The subband differential PMI maybe an index to indicate a difference between the recommended precoderand channel characteristics of the subband. In these embodiments, thesubband differential PMI may be based on a quantization error related toa difference between a DFT vector associated with the subband PMI andchannel characteristics of the subband.

In some embodiments, the first PMI report includes a first subband PMIand the second PMI report includes a second subband PMI. The first andsecond subband PMIs may be selected by the UE 202 to jointly describethe same subband of the channel. The first subband PMI and the secondsubband PMI correspond to precoding matrices selected by the UE 202 froma same codebook.

In some embodiments, the first and second PMI reports 103 are receivedfrom the UE 202 by the eNB 102 on a physical uplink control channel(PUCCH) within either a same subband-report subframe or a differentsubband-report subframe. In these embodiments, the PUCCH may beconfigured in accordance with 3GPP TS 36.213 V10.0 (referred to as LTErelease 10). Depending on the PUCCH format being used, the first andsecond PMI reports 103 may be received in the same subband-reportsubframe or a different subband-report subframe. In some otherembodiments, the first and second PMI reports 103 may be received on aphysical uplink shared channel (PUSCH).

In some embodiments, the first PMI report may be a wideband PMI reportand the second PMI report is a subband PMI report. In these embodiments,the wideband PMI report and the subband PMI report may correspond to thewideband PMI report and the subband PMI report as defined in LTE release10; however, both the wideband PMI report and the subband PMI report inaccordance with some embodiments of the present invention include a PMIdescribing the same subband. In these embodiments, both of the PMIsrelate to the same subband and may be used by the eNB 102 to determinean interpolated precoder matrix for a single subband.

In some embodiments, the codebook used by the UE 202 for selecting boththe first and second subband PMIs is a four transmit (4TX) antennacodebook, and the first and second PMI reports 103 are reported inaccordance with an eight transmit (8TX) antenna reporting mode (e.g.,for PUCCH 2-1). In these embodiments, the 4TX codebook may be the 4TXcodebook of LTE release 8 and the first and second PMI reports 103 maybe reported in accordance with the 8TX codebook of LTE release 10 on thePUCCH in format 2-1 (i.e., PUCCH 2-1).

In some embodiments, the single subband precoder matrix (i.e., theinterpolated precoding matrix) may be computed by performing aninterpolation on corresponding vectors of precoder matrices indicated bythe first subband PMI and the second subband PMI. The interpolation mayinclude weighting and combining the corresponding vectors of theprecoder matrices to generate an interpolated precoding matrix.

In some embodiments, the precoder matrices indicated by the firstsubband PMI and the second subband PMI are weighted equally. In otherembodiments, the precoder matrices indicated by the first subband PMIand the second subband PMI may be weighted different. The interpolationprocedure and the weighting may be predetermined and known by both theUE 202 and the eNB 102. In some embodiments, the weighting may beindicated by the UE 202 and reported along with the first and second PMIreports 103.

In some embodiments, the first subband PMI and the second subband PMIcorrespond to precoding matrices selected from the same codebook. Thecodebook may consist of a number of DFT vectors and a number of non-DFTvectors, such as those illustrated in FIG. 3. When both the first andsecond PMIs indicate DFT vectors, the DFT phase of the interpolatedprecoding matrix is generated from a weighted average of the DFT phasesof the DFT vectors. On the other hand, when either the first or thesecond PMI does not indicate a DFT vector, each element of the vectorsof the interpolated precoding matrix is generated from a weightedaverage of phases of corresponding elements of the DFT vectors.

In these embodiments, when both the first and second PMIs indicate DFTvectors, vectors of the interpolated precoding matrix may comprise DFTvectors. When either the first and second PMIs do not indicate a DFTvector, the vectors of the interpolated precoding matrix are notnecessarily DFT vectors.

In these embodiments, when both the first and second PMIs indicate DFTvectors, each DFT vector can be uniquely defined by one phase. The phaseof the interpolated DFT vector is a weighted average of the two phasesof the two DFT vectors indicated by the first and second subband PMIs.

On the other hand, for a transmission of rank one, if any precodervector associated with the first and second PMIs is not a DFT vector,then each element of the interpolated precoder is generated from aweighted average of the phases of the same element of both precoders.When both of the PMIs do not indicate DFT vectors (i.e., either PMI mayindicate a non-DFT vector), each element of the interpolated precoderwill be a weighted average of the phases of the same element of bothprecoding matrices (i.e., the precoding matrices indicated by the firstand second subband PMIs).

For a transmission of rank two, the first column of the interpolatedprecoder will be interpolated using the first column of two precoders.The second column of the interpolated precoder is partially interpolatedfrom the second column of the two precoders and partially calculated toensure the two columns of the interpolated precoder are orthogonal toeach other. A transmission of rank two may be a two-layer transmissionon two antenna ports. A transmission of rank two may use a precodingmatrix having two precoding vectors. A transmission of rank one, on theother hand, may be a single layer transmission on a single antenna portand may use a precoding matrix having a single precoding vector. Theseembodiments are discussed in more detail below.

In some embodiments, the precoding performed by the eNB 102 may comprisemultiplying symbols by the interpolated precoding matrix (i.e., thesingle subband precoder matrix 105) to generate an orthogonal frequencydivision multiple access (OFDMA) transmission. In MU-MIMO embodiments,the OFDMA transmission may be precoded for transmission to a pluralityof UEs using the computed single subband precoder matrix generated byinterpolation for each UE. In these embodiments, each UE may recommendan interpolated precoder matrix with first and second PMI reports thatrelate to a single subband.

Although embodiments are described herein in which the UE 202 generatesthe first and second PMI reports 103 for transmission to the eNB 102 toallow the eNB 102 to precode signals for transmission, the scope of theembodiments is not limited in this respect. In other embodiments, theeNB 102 may generate first and second PMI reports 103 for transmissionto the UE 202 to allow the UE 202 to precode signals for transmission tothe eNB 102.

In some embodiments in which the PUSCH is configured for reporting mode3-2 (PUSCH 3-2), two PMI reports may be provided for every twoconsecutive subbands of a plurality of N subbands. In these embodiments,a single precoding matrix for each subband may be generated byinterpolating the precoding matrices indicated by the two PMIs for eachsubband. In some of these PUSCH 3-2 embodiments, one wideband PMI may beprovided for every N subbands and one subband PMI may be provided foreach subband. The single precoding matrix may be computed for eachsubband based on the wideband PMI and the subband PMI for the associatedsubband. Various PUSCH 3-2 embodiments are discussed in more detailbelow.

FIG. 4 is a flow chart of a procedure for generating and reporting firstand second PMIs in accordance with some embodiments. Procedure 400 maybe performed by a receiver (e.g., UE 202 (FIG. 2)) that is configured togenerate first and second PMIs 103 (FIG. 1) for transmission to atransmitter (e.g., eNB 102 (FIG. 1)).

In operation 402, a first codebook search may be performed based onchannel information for the subband 403. The codebook search may resultin a first precoding matrix that maximizes throughput.

In operation 404, a second codebook search may be performed based on thefirst precoding matrix selected in operation 402 to identify a secondprecoding matrix. The second codebook search may use the same codebookas the first codebook search and may select vectors with minimal chordaldistances.

In operation 406, an interpolated precoding matrix is generated from thefirst and second precoding matrices. The interpolated precoding matrixis tested to determine if channelization error is reduced, compared withuse of the precoding matrix associated with the first precoding matrix.

Operation 408 determines if the channelization error is reduced. Whenthe channelization error is reduced, operation 410 is performed. Whenthe channelization error is not reduced, operations 406 and 408 arerepeated to identify a different second precoding matrix.

In operation 410, the second precoding matrix is selected.

In operation 412, first and second PMIs 103 associated respectfully withthe first and second precoding matrices, along with a subband channelquality indicator (CQI) for the subband and a rank indicator (RI)(indicating the transmission rank) are fed back to the transmitter(e.g., the eNB 102).

In some embodiments, the codebook search of operations 402 and 404 fortwo W₂ PMIs can be very similar to that of one W₂ PMI in LTE release 8.In these embodiments, the UE 202 may first search for the best W₂ PMI ias the best precoding vector within the original 4Tx LTE release 8codebook. After i is decided, the UE 202 may search j only in thematrices having minimum chordal distance with matrix i and test if theinterpolated matrix will result in higher codebook search metrics. Forexample in FIG. 3, the best W₂ PMI i is DFT vector 302 (vector 1) aftersearching the LTE release 8 codebook. And after fixing i=1, the UE 202may search two candidates of j (i.e., DFT vectors 304 (vector 4) and DFTvector 307 (vector 5)) and determine which of the resulting interpolatedprecoders for j=4 and j=5 will provide better metrics than DFT vector302 alone. In this example, the UE 202 may determine that DFT vector 304(j=4) will provide a better precoder than DFT vector 302 (i=1) alone. Inthis example, the UE 202 may feed back the first and second PMI reports103 indicating W₂ PMI i=1 and W₂ PMI j=4. The subband CQI may becalculated conditioned on the interpolated precoder from W₂ PMI i=1 andW₂ PMI j=4.

In some embodiments, the interpolated precoder may be calculated asfollows:

The first W₂ PMI may be i and the second W₂ PMI may be represented by j,then the precoder for PMI i and j are v_(i) and v_(j) respectively. Forrank one, both v_(i) and v_(j) are 4×1 vectors. In the case when iequals to j, then the recommended W₂ precoder is v_(i).

If both v_(i) and v_(j) are DFT vectors and i≠j, e.g. v_(i)=0.5[1 e^(jθ)^(i) e^(j2θ) ^(i) e^(j3θ) ^(i) ]^(T) and v_(j)=0.5[1 e^(jθ) ^(j) e^(j2θ)^(j) e^(j3θ) ^(j) ]T, then the recommended W₂ precoder is v_(W) ₂ =0.5[1 e^(j(θ) ^(i) ^(+θ) ^(j) ^()/2) e^(j(θ) ^(i) ^(+θ) ^(j) ⁾ e^(j3(θ)^(i) ^(+θ) ^(j) ^()/2)]^(T).

If any of the two precoding vectors are non-DFT vectors, e.g.v_(i)=0.5[1 e^(jα) ¹ e^(jα) ² e^(jα) ³ ]T and v_(j)=0.5 [1 e^(jβ) ¹e^(jβ) ² e^(jβ) ³ ]^(T), then the recommended W₂ precoder is

$v_{W_{2}} = {{0.5\begin{bmatrix}1 & ^{j\frac{({\alpha_{1} + \beta_{1}})}{2}} & ^{j\frac{({\alpha_{2} + \beta_{2}})}{2}} & ^{j\frac{({\alpha_{3} + \beta_{3}})}{2}}\end{bmatrix}}^{T}.}$

In accordance with some embodiments at least for rank one, an additionalwideband rank one PMI may be used to report a second-best PMI, and thewideband precoder may be interpolated from two wideband PMI as describedabove. The subband CQI may be conditioned on the wideband precoderinterpolated by both wideband rank one PMI.

Table 1 shows some example system level throughput gains for the PUSCHin extended reporting mode 3-1 with two wideband PMIs compared with thePUSCH mode 3-1. In these embodiments, the CQI calculation may be thesame as described in LTE release 8.

TABLE 1 Mode 3-1 extension with two WB PMI compared with Mode 3-1 highangular spread Tx |||| Rx || Tx XX Rx+ Tx X X Rx+ Cell SE gain 8.6% 2.8%1.6% %5 SE gain  16% 6.5% −2.6%

Unlike PUSCH 3-1, PUSCH 3-2 transmissions may feedback one subband PMIper subband, allowing PUSCH 3-2 to address channels with greater delayspread. One issue is that PUSCH 3-2 may not provide enough throughputgain over PUSCH 3-1, particularly for a spatial-channel model (SCM) inan urban-macro-cell environment. Table 2 illustrates a comparisonbetween PUSCH 3-1 and PUSCH 3-2.

TABLE 2 PUSCH Mode 3-2 compared with Mode 3-1 high angular spread Tx|||| Rx || Tx XX Rx+ Tx X X Rx+ Cell SE gain   1% 2.8% 3.5% %5 SE gain−0.2% 5.3% −0.1%

In accordance with some embodiments, for every two consecutive subbands,two PMIs may be reported for two consecutive subbands and the precodersof two consecutive subbands may be interpolated from the two reportedPMIs. The CQI calculation may be conditioned on the interpolatedprecoder. The overall signalling may be the same as the straight forwardPUSCH 3-2.

Table 3 shows the throughput gain for these embodiments compared withthe straight forward PUSCH 3-2.

TABLE 3 PUSCH Mode 3-2 extension with two PMIs for two subbands comparedwith PUSCH Mode 3-2 high angular spread Tx |||| Rx || Tx XX Rx+ Tx X XRx+ Cell SE gain   9% 3.5% 0.2% %5 SE gain 7.8% 0.9%  14%

As can be seen from table 3, compared with straight forward PUSCH 3-2,sending two PMIs for two subbands and using an interpolated precoder tocalculate the CQI results in a significant throughput gain without anincrease in the signaling overhead. For PUSCH 3-2, a reduction insubband PMI overhead may allow a modified PUSCH 3-2 (i.e., with lessoverhead) to be competitive with PUSCH 3-1.

In some embodiments, to reduce overhead half of subband PMIs may be sentwith each subband PMI and may cover two consecutive subbands. Table 4compares the performance in terms of spectrum efficiency (SE) with onePMI per subband for straight forward PUSCH 3-2.

TABLE 3 high angular spread Tx |||| Rx || Tx XX Rx+ Tx X X Rx+ Cell SEgain −0.3% −0.9% −0.7% %5 SE gain   −3% −0.2% −0.4%

Spectrum efficiency may be described in bits/s/Hz. For example if a one10 MHz system bandwidth is able to deliver 10M bits in one second, theSE is 1 bit/s/Hz. As illustrated in table 4, sending one PMI for twoconsecutive subbands results in a marginal reduction in spectrumefficiency compared with one subband PMI per subband. Thus most of thegain in straight forward PUSCH 3-2 is retained.

In some alternate embodiments, one wideband PMI may be sent, and foreach subband, a 2-bit differential subband PMI may be sent. The top fourprecoders having the smallest chordal distance to the wideband PMI maybe listed by the 2 bits of the differential subband PMI. The precoderfor each subband may be interpolated by the wideband PMI and the subbandPMI. Table 5 shows one wideband PMI plus two differential PMIs persubband compared with one subband PMI for two consecutive subbands.

TABLE 5 high angular spread Tx |||| Rx || Tx XX Rx+ Tx X X Rx+ Cell SEgain  8.7%  2.7%  0.1% %5 SE gain −10% −13% −11%

As can be seen from table 5, compared with one subband PMI covering twoconsecutive subbands, sending one wideband PMI and one differentialsubband PMI and using precoder interpolation provides significant gainsin cell throughput. Thus, extending the PUSCH based on CQI reporting for4Tx antenna transmissions with precoder interpolation for rank one mayprovide a significant throughput gain for MU-MIMO transmissions. Inaccordance with embodiments, for the PUSCH 3-1 extension, one morewideband PMI may be fed back for 4Tx at least for rank one. The subbandCQI is calculated conditioned on the interpolated precoder using bothwideband PMI.

In accordance with embodiments, for the PUSCH 3-2, for an overhead ofone PMI per subband, two PMIs may be used to interpolate the precoderfor two consecutive subbands and calculate the CQI for these twosubbands accordingly. For an overhead of one PMI every two subbands, onewideband PMI and 2 bits differential PMI per subband may be used tointerpolate the precoder for each subband and calculate the CQI for thissubband conditioned on the interpolated precoder.

FIGS. 5A and 5B illustrate examples of transmissions on the PUCCH 2-1 inaccordance with some embodiments. FIG. 5A shows an example of the PUCCH2-1 in which eight transmit antennas (8Tx) are used at the eNB 102 (FIG.1). Because the 8Tx codebook in LTE-A release 10 is much larger than 4Txcodebook in LTE release 8, two PMIs may be used to represent oneprecoder. For rank one, the first index may be 4 bits and the secondindex may also be 4 bits. The two index codebook structure may result inerror propagation because if the first precoding matrix (W₁) is inerror, the subsequent precoding matrix using W₂ report would also be inerror.

FIG. 5B shows an example of the PUCCH 2-1 in which four transmit (4Tx)antennas are used at the eNB 102. In this example, there is nopayload-type identifier (PTI) bit in a 4Tx antenna transmission and thusthere is no error propagation from the wideband precoding index to thesubband precoder. On the other hand, in case of an 8Tx antennatransmission and a CQI report in accordance with PUCCH 2-1, the PTI bitis sent together with RI. The PTI bit determines the content of reportsfollowing the RI/PTI report, so the PTI may be in error.

FIGS. 6A-6G illustrate PMI and CQI reporting associated with the PUCCH3-2 in accordance with embodiments. FIG. 6A illustrates an example of aPUCCH 3-2 using 8 transmit antennas at the eNB 102 (FIG. 1). Because the8Tx codebook in LTE-A release 10 is much larger than 4Tx codebook in LTErelease 8, two PMIs may be used to represent one precoder. One widebandW₁ PMI may be signaled and one subband W₂ PMI may be signaled for eachsubband. The subband precoder may be represented by both the wideband W₁PMI and the subband W₂ PMI. For rank one, the wideband W₁ PMI may be 4bits and subband W₂ PMI may also be 4 bits.

FIG. 6B illustrates an example of a straight-forward PUCCH 3-2 for 4Tx.Since there is no wideband W₁ PMI for 4Tx, the precoder for each subbandmay be represented by the subband W₂ PMI alone. For 4Tx, the throughputof each subband may be limited by the residual CSI quantization errorfrom the LTE release 8 codebook. If the channel is less frequencyselective, the use of a subband PMI does not improve the throughoutsignificantly compared with the use of a subband PMI on the PUSCH 3-1.

Although the use of a larger codebook may improve throughputsignificantly, defining a larger codebook may not be feasible in LTErelease 10 when the LTE release 8 4Tx codebooks are used. Therefore,embodiments disclosed herein that use using the release 8 codebooks toachieve a higher resolution may be particularly beneficial.

In accordance with these embodiments, a wideband W₂ PMI is signaled forthe 4Tx PUSCH 3-2, and both the wide band W₂ PMI report and the subbandW₂ PMI report may be used to calculate the precoder for each subband.The subband CQI is calculated according to the interpolated subbandprecoder. FIG. 6C illustrates the use of one wideband W₂ PMI and onesubband W₂ PMI to generate an interpolated subband precoder. In thisexample the wideband W₂ PMI indicates DFT vector 1 and the subband W₂PMI indicates DFT vector 4. FIG. 6D illustrates reporting for 4Tx PUSCH3-2 (i.e., one wideband PMI for all subbands) in accordance withembodiments. From a size perspective, the reporting for 4Tx PUSCH 3-2 isthe same as the reporting for the 8Tx report type. FIG. 6E illustratesreporting for 4Tx PUSCH 3-2 in which a subband W₂ PMI is reported forevery two subbands along with a wideband W₂ PMI.

Instead of sending one wideband W₂ PMI and sending one subband W₂ PMIfor each subband, some alternate embodiments include sending two W₂ PMIsfor every two consecutive subbands. In these embodiments, the precoderfor these two subbands may be interpolated by these two W₂ PMI reports.An example of this is illustrated in FIG. 6F.

Other alternative embodiments may include sending one wideband W₂ PMIevery N subbands and sending one subband W₂ PMI for every subband. Inthese embodiments, the precoder for each subband may be jointlyinterpolated from both the wideband W₂ PMI for this subband and thesubband W₂ PMI for this subband. An example of this is illustrated inFIG. 6G.

In these embodiments, the subband precoder may be calculated as follows.If the wideband W₂ PMI is represented as i and the subband W₂ PMI isrepresented as j, then the precoder for PMI i and j are v_(i) and v_(j).For rank one, both v_(i) and v_(j) are 4 by 1 vectors. Note that if j isequal to i, then the recommended subband precoder is v_(i).

If both v_(i) and v_(j) are DFT vectors, which have the forms v_(i)=½[1e^(jθ) ^(i) e^(j2θ) ^(i) e^(j3θ) ^(i) ]^(T) and v_(j)=½[1 e^(jθ) ^(j)e^(j2θ) ^(j) e^(j3θ) ^(j) ]^(T), then the recommended subband precodermay be computed as

$v_{SB} = {{\frac{1}{2}\begin{bmatrix}1 & ^{j\frac{\beta_{i} + {\mu \; \beta_{j}}}{1 + \mu}} & ^{j\; 2{(\frac{\beta_{i} + {\mu \; \beta_{j}}}{1 + \mu})}} & ^{j\; 3{(\frac{\beta_{i} + {\mu \; \beta_{j}}}{1 + \mu})}}\end{bmatrix}}^{T}.}$

When any of the two precoding vectors are non-DFT vectors v_(i)=½[1e^(jα) ¹ e^(jα) ² e^(jα) ³ ]^(T) and v_(i)=½[1 e^(jβ) ¹ e^(jβ) ² e^(jβ)³ ]^(T), then the recommended subband precoder may be computed as

$v_{SB} = {\frac{1}{2}\begin{bmatrix}1 & ^{j\frac{({\alpha_{1} + {\mu \; \beta_{1}}})}{1 + \mu}} & ^{j\frac{({\alpha_{2} + {\mu \; \beta_{2}}})}{2 + \mu}} & ^{j\frac{({\alpha_{3} + {\mu \; \beta_{3}}})}{3 + \mu}}\end{bmatrix}}^{T}$

In these embodiments, μ is a phase scaling factor and may, for example,be either 1 or ½. The wideband and the subband precoding matrixes may berepresented by

$v_{i} = {{{\frac{1}{2\sqrt{2}}\begin{bmatrix}1 & ^{j\; \alpha_{4}} \\^{j\; \alpha_{1}} & ^{j\; \alpha_{5}} \\^{j\; \alpha_{2}} & ^{j\; \alpha_{6}} \\^{j\; \alpha_{3}} & ^{j\; \alpha_{7}}\end{bmatrix}}^{T}\mspace{14mu} {and}\mspace{14mu} v_{j}} = {\frac{1}{2\sqrt{2}}\begin{bmatrix}1 & ^{j\; \beta_{4}} \\^{j\; \beta_{1}} & ^{j\; \beta_{5}} \\^{j\; \beta_{2}} & ^{j\; \beta_{6}} \\^{j\; \beta_{3}} & ^{j\; \beta_{7}}\end{bmatrix}}^{T}}$

The recommended matrix may be computed as

$v_{i} = {\frac{1}{2\sqrt{2\left( {1 + ɛ^{2}} \right)}}\begin{bmatrix}1 & {ɛ\; ^{\frac{j{({\alpha_{4} + {\mu \; \beta_{4}}})}}{2}}} \\^{\frac{j{({\alpha_{1} + \beta_{1}})}}{2}} & {ɛ\; ^{\frac{j{({\alpha_{5} + {\mu \; \beta_{5}}})}}{2}}} \\^{\frac{j{({\alpha_{2} + \beta_{2}})}}{2}} & {{- ɛ}\; ^{\frac{j{({\alpha_{2} + \beta_{2} + \alpha_{4} + {\mu \; \beta_{4}}})}}{2}}} \\^{\frac{j{({\alpha_{3} + \beta_{3}})}}{2}} & {{- ɛ}\; ^{\frac{j{({\alpha_{3} + \beta_{3} - \alpha_{2} - \beta_{2} + \alpha_{5} + {\mu \; \beta_{5}}})}}{2}}}\end{bmatrix}}^{T}$

In these embodiments, ε may be used as a scalar between 0 and 1 for thesecond layer if the secondary principle Eigen value is considerablysmaller than that of the principle Eigen value. In these embodiments, εmay be set to equal 1. In some embodiments, ε may be signaled by eNB 102(FIG. 1). The signaling can be either cell-specific or UE specific. μ isthe phase scaling factor for the second precoder and may have a valuebetween 0 and 1.

In some embodiments, the subband CQI calculation may be conditioned onsubband W₂ PMI j. The eNB 102 may adjust the subband precoder and therelated subband CQI based on the subband W₂ PMI j and wideband W₂ PMI iin a purely implementation-related manner.

In these embodiments, the codebook search method for wideband W₂ PMI iand the subband W₂ PMI j may be similar to that of the LTE release 8implementation. In these embodiments, the UE 202 (FIG. 2) may firstsearch for a wideband W₂ PMI i as the best precoding vector within theoriginal 4Tx LTE release 8 codebook in the wide band W₂/CQI report. TheUE 202 may then search for a subband W₂ j within the vectors havingminimum chordal distance with vector i and test if the interpolatedvector results in higher codebook search metrics for the given subbandin the subband W₂/CQI report. For example in FIG. 6C, the best widebandW₂ PMI i may be DFT vector 1 after searching the release 8 codebook. Andafter fixing wideband W₂ PMI i=1, the UE 202 may search three candidatesfor j which may be DFT vectors 1, 4 and 5. The UE 202 may then test eachof the interpolated subband precoders (i.e., for j=1, j=4 and j=5) todetermine which will provide the best metrics for the given subband. Inthis case, the UE 202 may determine that j=4 will result in the bestprecoder for the given subband. In these embodiments, the UE 202 mayfeed back the subband W₂ PMI j=4. The subband CQI will therefore beconditioned on the interpolated subband precoder from wideband W₂ PMIi=1 and subband W₂ PMI j=4.

In these embodiments, with the subband precoder being interpolated basedon the wideband W₂ PMI i and the subband W₂ PMI j, the CSI quantizationerror for the given subband may be effectively halved when a highlycorrelated channel is considered and the speed of the UE 202 is low.

Since one subband W₂ PMI should be sent for each subband in PUSCH 3-2 toreduce quantization error, the subband PMI overhead reduction becomes avalid consideration. Two kinds of subband W₂ PMI reduction embodimentscan be defined.

In a first embodiment, a 2-bits subband W₂ differential PMI to signalthe subband W₂ may be defined. These 2-bits subband W₂ differential PMImay be sufficient to describe the top four candidates from the LTErelease 8 codebook to perform subband precoder interpolation.

For 4Tx, the subband W₂ differential PMI may be defined using thefollowing tables:

TABLE 6-4 4Tx Rank one Subband W₂ differential PMI Wideband W₂ PMI index0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Subband 0 0 1 2 3 4 5 6 7 8 9 1011 12 13 14 15 W₂ 1 7 4 5 6 0 1 2 3 1 0 1 0 4 5 5 4 differential 2 4 5 67 1 2 3 0 3 2 3 2 7 6 6 7 PMI index 3 9 8 11 10 8 9 10 11 7 4 5 6 8 9 1011

TABLE 6-5 4Tx Rank two Subband W₂ differential PMI Wideband W₂ PMI index0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Subband 0 0 1 2 3 4 5 6 7 8 9 1011 12 13 14 15 W₂ 1 1 0 1 0 5 4 0 0 1 0 4 4 0 0 0 0 differential 2 3 2 32 10 10 9 9 3 2 5 5 1 1 1 1 PMI index 3 6 8 9 8 11 11 10 10 9 6 6 6 3 22 3

TABLE 6-6 4Tx Rank 3 Subband W₂ differential PMI Wideband W₂ PMI index 01 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Subband 0 0 1 2 3 4 5 6 7 8 9 10 1112 13 14 15 W₂ 1 1 0 9 0 7 6 5 4 9 2 1 2 6 4 7 5 differential 2 3 10 1110 1 1 0 2 11 8 3 8 5 7 4 6 PMI index 3 6 6 7 12 8 11 11 11 6 12 7 6 1 11 1

In a second embodiment, the granularity for each subband W₂ PMI may bereduced such that one subband W₂ will correspond to N neighboringsubbands. N for example may be two. An example of this was illustratedin FIG. 6E. The precoder for two neighboring subbands may beinterpolated based on the subband W₂ PMI for those two subbands and thewideband W₂ PMI.

Although the eNB 102 (FIG. 1) and the UE 202 (FIG. 2) are illustrated ashaving several separate functional elements, one or more of thefunctional elements may be combined and may be implemented bycombinations of software-configured elements, such as processingelements including digital signal processors (DSPs), and/or otherhardware elements. For example, some elements may comprise one or moremicroprocessors, DSPs, application specific integrated circuits (ASICs),radio-frequency integrated circuits (RFICs) and combinations of varioushardware and logic circuitry for performing at least the functionsdescribed herein. In some embodiments, the functional elements of theeNB 102 and the UE 202 may refer to one or more processes operating onone or more processing elements.

Embodiments may be implemented in one or a combination of hardware,firmware and software. Embodiments may also be implemented asinstructions stored on a computer-readable storage device, which may beread and executed by at least one processor to perform the operationsdescribed herein. A computer-readable storage device may include anynon-transitory mechanism for storing information in a form readable by amachine (e.g., a computer). For example, a computer-readable storagedevice may include read-only memory (ROM), random-access memory (RAM),magnetic disk storage media, optical storage media, flash-memorydevices, and other storage devices and media. In some embodiments, theeNB 102 and the UE 202 may include one or more processors and may beconfigured with instructions stored on a computer-readable storagedevice.

The Abstract is provided to comply with 37 C.F.R. Section 1.72(b)requiring an abstract that will allow the reader to ascertain the natureand gist of the technical disclosure. It is submitted with theunderstanding that it will not be used to limit or interpret the scopeor meaning of the claims. The following claims are hereby incorporatedinto the detailed description, with each claim standing on its own as aseparate embodiment.

1. (canceled)
 2. An apparatus of a User Equipment (UE) comprising:memory; and processing circuitry configured to encode symbols fortransmission in a physical uplink shared channel (PUSCH), wherein theprocessing circuitry is configured to: decode configuration informationfor channel state information (CSI) reporting; configure the HE for theCSI reporting in accordance with PUSCH CSI reporting mode 3-2 (PUSCH3-2) based on the configuration information; select a preferredprecoding matrix for each subband of a set of subbands based on atransmission in a corresponding subband; report one wideband channelquality indicator (CQI) value of a precoder codebook for the set ofsubbands in accordance with the PUSCH 3-2; and report a single precodingmatrix indicator (PMI) for each subband, each reported single PMI beingassociated with the selected preferred precoding matrix for thecorresponding subband in accordance with the PUSCH 3-2, the PMI for eachsubband being selected from a four transmit antenna (4TX) codebook forreceipt of up to a four layer MIMO transmission.
 3. The apparatus ofclaim 2 wherein the processing circuitry is further configured to:decode configuration information for aperiodic channel state information(CSI) reporting using the PUSCH to configure the UE for PUSCH CSIreporting mode 3-1 (PUSCH 3-1); and when configured for the PUSCH 3-1;the UE is configured to: select a single precoding matrix from the 4TXcodebook for transmission on a plurality of subbands; report a singlePMI when configured for a four layer MIMO transmission; and report firstand second PMIs corresponding to the single precoding matrix whenconfigured for receipt of an eight layer MIMO transmission.
 4. Theapparatus of claim 2 wherein the processing circuitry is furtherconfigured to: report a subband CQI value for each subband, the reportedsubband CQI value reflecting transmission over a single subband usingthe selected preferred precoding matrix in the corresponding subband inaccordance with PUSCH 3-2, and wherein each of the subband CQI values isdifferentially encoded with respect to the wideband CQI value.
 5. Theapparatus of claim 4 wherein the processing circuitry is furtherconfigured to: report a rank indicator (RI) corresponding to atransmission rank; and calculate the single PMI for each subband and thesubband CQI value for each subband based at least in part on thereported rank indicator.
 6. The apparatus of claim 5 wherein theprocessing circuitry is further configured to decode the up to a fourlayer MIMO transmission from an enhanced Node B (eNB), the up to a fourlayer MIMO transmission precoded in accordance with the reported PMIs.7. The apparatus of claim 5 wherein the PMI for each subband is selectedfrom the 4TX codebook for receipt of up to an eight layer MIMOtransmission, each PMI corresponding to a pair of codebook indices. 8.The apparatus of claim 7 wherein the processing circuitry is furtherconfigured to decode the up to an eight layer MIMO transmission from anenhanced Node B (eNB), the up to an eight layer MIMO transmissionprecoded in accordance with the reported PMIs.
 9. The apparatus of claim4 wherein the processing circuitry is further configured to configurethe UE to report two or more subband CQI values for each subband.
 10. Anon-transitory computer readable storage medium that stores instructionsfor execution by processing circuitry of a User Equipment (UE) toconfigure the UE to: decode configuration information for channel stateinformation (CSI) reporting; configure the UE for the CSI reporting inaccordance with a physical uplink shared channel (PUSCH) PUSCH CSIreporting mode based on the configuration information, when the UE isconfigured for PUSCH CSI reporting mode 3-2 (PUSCH 3-2), the processingcircuitry is configured to: select a preferred precoding matrix for eachsubband of a set of subbands; report one wideband channel qualityindicator (CQI) value of a precoder codebook for the set of subbands inaccordance with the PUSCH 3-2; and report a single precoding matrixindicator (PMI) for each subband, each reported single PMI beingassociated with the selected preferred precoding matrix for thecorresponding subband in accordance with the PUSCH 3-2, the PMI for eachsubband being selected from a four transmit antenna (4TX) codebook forreceipt of up to a four layer MIMO transmission, and decode the up to afour layer MIMO transmission from an enhanced Node B (eNB), the up to afour layer MIMO transmission precoded in accordance with the reportedPMIs.
 11. The non-transitory computer readable storage medium of claim10 wherein when configured for PUSCH CSI reporting mode 3-2, theprocessing circuitry is further configured to: report a subband CQIvalue for each subband, the reported subband CQI value reflectingtransmission over a single subband using the selected preferredprecoding matrix in the corresponding subband in accordance with thePUSCH 3-2.
 12. The non-transitory computer readable storage medium ofclaim 11 wherein when configured for the PUSCH 3-2, the processingcircuitry is further configured to: report a rank indicator (RI)corresponding to a transmission rank; and calculate the single PMI foreach subband and the subband CQI value for each subband based at leastin part on the reported rank indicator.
 13. The non-transitory computerreadable storage medium of claim 12 wherein the PMI for each subband isselected from a four transmit antenna (4TX) codebook for receipt of upto a four layer MIMO transmission.
 14. The non-transitory computerreadable storage medium of claim 12 wherein the PMI for each subband isselected from a four transmit antenna (4TX) codebook for receipt of upto an eight layer MIMO transmission, each PMI corresponding to a pair ofcodebook indices.
 15. The apparatus of claim 11 wherein the one or moreprocessors are configured to configure the UE to report two or more ofthe subband CQI values for each subband when configured for the PUSCH3-2.
 16. An apparatus of an enhanced Node B (eNB) comprising: memory andprocessing circuitry configured to: generate configuration informationto user equipments (UEs) for channel state information (CSI) reportingusing a physical uplink shared channel (PUSCH); and encode theconfiguration information for transmission to the UEs, wherein for UEsconfigured for reporting in accordance with PUSCH CSI reporting mode 3-2(PUSCH 3-2), the processing circuitry is configured to: decode onewideband channel quality indicator (CQI) value of a precoder codebookfor a set of subbands; decode a reported single precoding matrixindicator (PMI) for each subband of the set of subbands, each reportedsingle PMI being associated with a selected preferred precoding matrixfor a corresponding subband; decode a subband CQI value for eachsubband, the reported subband CQI value reflecting transmission over asingle subband using the selected preferred precoding matrix in thecorresponding subband; and encode up to a four layer multi-user MIMO(MU-MIMO) transmission for the UEs in accordance with the reported PMIS.17. The apparatus of claim 16 wherein the CQIs values and PMIs arereceived from UEs on a physical uplink control channel (PUCCH), andwherein the up to a four layer MU-MIMO transmission is configured for aphysical downlink shared channel (PDSCH).
 18. The apparatus of claim 17wherein the PMI for each subband is associated with a four transmitantenna (4TX) codebook for preceding of up to a four layer MIMOtransmission.
 19. The apparatus of claim 17 wherein the PMI for eachsubband is associated with a four transmit antenna (4TX) codebook for upto an eight layer MIMO transmission, each PMI corresponding to a pair ofcodebook indices.
 20. The apparatus of claim 16 wherein the processingcircuitry is configured to decode a reported two or more of the subbandCQI values for each subband.